Levin E M, Cui J-F, Schmidt-Rohr K
Division of Materials Sciences and Engineering, Ames Laboratory U.S. Department of Energy (DOE), Ames, IA 50011, USA; Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
Department of Chemistry, Iowa State University, Ames, IA 50011, USA.
Solid State Nucl Magn Reson. 2016 Sep;78:40-44. doi: 10.1016/j.ssnmr.2016.07.003. Epub 2016 Jul 16.
(125)Te NMR spectra and spin-lattice relaxation times, T1, have been measured for several GeTe-based materials with Te excess. The spectra show inhomogeneous broadening by several thousand ppm and a systematic variation in T1 relaxation time with resonance frequency. The quadratic dependence of the spin-lattice relaxation rate, 1/T1, on the Knight shift in the Korringa relation is found to be valid over a wide range of Knight shifts. This result confirms that T1 relaxation in GeTe-based materials is mostly dominated by hyperfine interaction between nuclei and free charge carriers. In GeTe with 2.5% excess of Te, about 15% of the material exhibits a Knight shift of ≥4500ppm and a T1 of only 0.3ms, indicating a high hole concentration that could correspond to close to 50% vacancies on the Ge sublattice in this component. Our findings provide a basis for determining the charge carrier concentration and its distribution in complex thermoelectric and phase-change tellurides, which should lead to a better understanding of electronic and thermal transport properties as well as chemical bonding in these materials.
已对几种富碲的基于GeTe的材料测量了核磁共振（NMR）谱和自旋晶格弛豫时间T1。这些谱显示出几千ppm的非均匀展宽以及T1弛豫时间随共振频率的系统性变化。发现自旋晶格弛豫率1/T1对科林加关系中奈特位移的二次依赖性在很宽的奈特位移范围内都是有效的。这一结果证实，基于GeTe的材料中的T1弛豫主要由原子核与自由电荷载流子之间的超精细相互作用主导。在碲过量2.5%的GeTe中，约15%的材料表现出≥4500ppm的奈特位移和仅0.3ms的T1，这表明空穴浓度很高，在该组分中可能对应于Ge亚晶格上接近50%的空位。我们的研究结果为确定复杂热电和相变碲化物中的载流子浓度及其分布提供了基础，这将有助于更好地理解这些材料中的电子和热传输特性以及化学键合。
